This application is based upon and claims priority of Japanese Patent Applications No. 2001-10423, filed in Jan. 18, 2001, and 2001-172960, filed in Jun. 7, 2001, and No. 2001-67615, filed in Mar. 9, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a solder jointing system and a solder jointing method and, more particularly, a solder jointing system and a solder jointing method employed to joint the solder layer to wirings or pads of the semiconductor device or the electronic device.
The present invention relates to a semiconductor device manufacturing method and a semiconductor device manufacturing system and, more particularly, a semiconductor device manufacturing method and a semiconductor device manufacturing system having a step/means for removing unnecessary substance that is adhered onto a surface of the electrode or the wiring formed mainly of copper.
In the prior art, normally the wiring or the electrode of the semiconductor device is made of metal containing mainly aluminum. However, in recent years, in order to satisfy requests for the miniaturization of the wirings and the higher speed, the development of the practical implementation of the wiring that employs the copper having the small resistivity and the high electromigration resistance as main material is being proceeded.
This copper has the property that is reduced more easily than aluminum, but is oxidized easily. Accordingly, in the steps of manufacturing the semiconductor device, the technology of removing quickly and precisely the oxide film formed on the surface of the copper wiring or the copper electrode to clean the surface is requested.
2. Description of the Prior Art
As the method of jointing the solder to the metal pattern such as the electrode pad, the metal wiring, etc. of the semiconductor device, the method of forming the solder on the metal pattern by virtue of the plating method, the printing method, the ball mounting method, etc. and then heating/melting the solder to joint/shape it onto the electrode pad is employed.
In melting the solder, normally the oxide film on the surface of the solder or the electrode pad under the solder is removed by using the flux, and then the solder is melted and jointed while cleaning the surface.
The solder jointing step using the flux is carried out by the method described hereunder, for example.
First, the flux that is coated on the surface of the metal pattern as the solder-deposited surface covers the surface of the metal pattern to prevent the oxidation of the metal pattern while its surface is being activated by the heating, so that the activated state of the metal pattern is maintained. At the same time, the solder is melted to spread over the surface of the metal pattern. A part of the flux is dissolved by the melting of the solder.
Then, the solder is solidified by the cooling and is jointed to the surface of the metal pattern. At the same time, the flux and the dissolved product remaining on the metal pattern are also solidified.
After the solder joint using such flux is executed, the solidified flux is removed by the cleaning. In this case, since the dissolved product cannot be simply removed by the organic solvent not-containing flon or trichlene in this cleaning, a large quantity of organic solvent must be used in this cleaning.
However, since the organic solvent exerts a harmful influence upon the environment, the development of the solder jointing method that does not need the cleaning is desired.
Also, in the packaging step of the electronic parts module, normally the packaging step is applied after the flux or the flux-containing paste is coated on the solder-jointed portion. In such case, since the flux is dissolved by the heat applied in the packaging to thus generate the harmful gas, the safety of the operation must be assured. Also, if the halogen component remains in the module as the residue of the flux, corrosion of the wirings in the module and the migration of the wirings are accelerated. Therefore, the thorough cleaning is needed, which acts as the cause to bring about the increase of the fabrication cost.
In order to overcome these problems, following methods or equipments are known.
First, the soldering method using the carboxylic acid is set forth in Patent Application Publication (KOKAI) Hei 6-190584 (literature 1), Patent Application Publication (KOKAI) Hei 6-267632 (literature 2), and Patent Application Publication (KOKAI) Hei 7-164141(literature 3), for example. Also, the equipment is set forth in literature 3.
Also, the soldering method executed in the low pressure or vacuum atmosphere is set forth in Patent Application Publication (KOKAI) Hei 4-220166 (literature 4), Patent Application Publication (KOKAI) Hei 5-211391 (literature 5), Patent Application Publication (KOKAI) Hei 6-29659 (literature 6), Patent Application Publication (KOKAI) Hei 7-79071 (literature 7), and Patent Application Publication (KOKAI) Hei 7-170063 (literature 8).
However, according to the solder jointing system and the solder jointing method in the prior art, there are subjects described in the following.
First, the first subject is that the danger of the explosion in the solder jointing atmosphere is present.
For example, it is set forth in the literature 3 that, in the solder jointing system using the carboxylic acid and the diketone, the carboxylic acid gas is supplied to reduce the oxide film of the solder and also the droplet of the diketone is supplied to remove the oxide film of the pad. However, the diketone is such material that is expensive as set forth in the literature 3 and has the danger of the explosion. Both the diketone and the carboxylic acid have the explosive limit. If the temperature and the concentration in the processing layer and the oxygen concentration exceed respective certain ranges, e.g., if the formic acid concentration and the oxygen concentration reach 30% and 10% at the temperature of 100xc2x0 C. respectively, there exists the danger of the explosion.
The equipment and the method that have the possibility to reach such conditions causing the danger of the explosion are not readily accepted.
The second subject is that the carboxylic acid has the poisonous property.
For example, as disclosed in the literature 4, in order to prevent the leakage of the carboxylic acid from the process area, it is advantageous to execute the soldering by introducing the carboxylic acid into the chamber, that is excluded from the air, while reducing the oxide film. However, the solder joint in the chamber has small processing capability.
The third subject is that the re-oxidation is caused by the carboxylic acid that still remains on the surface of the solder and the surface of the metal pattern after the solder joint.
According to the examination of the inventors of the present invention, if the component of the carboxylic acid still remains on the surface of the solder, the surface of the solder is oxidized again after the solder is left as it is for a predetermined time in the atmosphere. Also, if the oxygen concentration of the atmosphere in which the solder joint is carried out is high, the surface of the solder is oxidized again by the residual heat after the heating/melting.
The fourth subject is that the throughput of the solder joint must be improved in the well-known solder jointing system.
The solder is formed on the wiring or the pad of the semiconductor substrate, the ceramic substrate, the circuit board, etc., then is carried into the solder jointing system, and then is heated/melted there to be jointed to the wiring or the pad. Since the substrate is loaded/unloaded one by one into/from the solder jointing system, i.e., such solder jointing system has the so-called sheet-fed processing structure, efficiency of the solder joint is low. For this reason, in order to enhance the substrate processing capability, the solder jointing system in which a plurality of neighboring solder joint areas are provided is set forth in FIG. 2 and FIG. 3 of Patent Application Publication (KOKAI) Hei 11-233934. In this case, since this equipment is substantially equivalent to the employment of a plurality of solder jointing systems, not only the cost is increased but also the wide area is needed.
The fifth subject is that the generation of residue on the substrate must be prevented after the solder joint. In above Patent Application Publication (KOKAI) Hei 7-164141, it is set forth that the mixture of the carboxylic acid and the diketones is introduced into the solder melting area in the solder jointing. In this case, the mixture which is supplied to the solder melting area in the form of the droplet is ready to generate the residue on the substrate.
In the prior art, in the step of manufacturing the semiconductor device having the electrode or the wiring containing the copper as the major material (the electrode and the wiring are referred to collectively as the xe2x80x9ccopper wiring, etc.xe2x80x9d hereinafter), the cleaning step must be carried out as {circle around (1)} the post-process of the chemical mechanical polishing (referred to as xe2x80x9cCMPxe2x80x9d hereinafter) step of the wiring in the semiconductor device, {circle around (2)} the pre-process of the physical vapor deposition (referred to as xe2x80x9cPVDxe2x80x9d hereinafter) process or the chemical vapor deposition (referred to as xe2x80x9cCVDxe2x80x9d hereinafter) process for the semiconductor substrate, {circle around (3)} the post-process of the etching process, {circle around (4)} the pre-process of the packaging process, etc. The cleaning steps in respective processes will be explained hereunder.
{circle around (1)} The Cleaning Step as the Post-process of the CMP Step
As the cleaning method carried out after the CMP step of the copper wiring, etc. is completed, there is the method employing the carboxylic acid as the oxidizing material, like Patent Application Publication (KOKAI) Hei 11-33023, etc., as known in the prior art. This method executes previously the cleaning in the acid atmosphere after the cleaning in the alkaline atmosphere. In addition, there are many well-known examples about the method and the equipment employing the carboxylic acid as the oxidizing material, like the disclosure in Patent Application Publication (KOKAI) Hei 8-83780, etc.
Normally, as the cleaning carried out after the CMP step of the copper wiring, etc. is completed, the step of removing the particles by the brush scraper and the step of removing the copper oxide formed on the copper oxide and the copper wiring, etc. on the insulating layer by the chemicals are performed. The chemicals such as the citric acid, the oxalic acid, the hydrogen fluoride, etc., that can remove the copper oxide but has the small etching action against the copper are selected.
{circle around (2)} The Cleaning Step as the Pre-process of the PVD Process and the CVD Process
As the oxide film removing method in the physical or chemical vapor deposition step, there is the method of removing the oxide film by the reducing gas plasma, like the disclosure in Patent Application Publication (KOKAI) Hei 9-82798, for example. According to this method, the copper wiring, etc. are cleaned by the inverse sputter using the mixed gas containing the hydrogen gas.
Also, in Patent Application Publication (KOKAI) Hei 9-232313 there is set forth the method of forming the copper wiring, etc. uniformly by cleaning the surface by using the reducing (hydrogen) gas when the copper wiring, etc. are formed. In addition, as set forth in Patent Application Publication (KOKAI) Hei 8-316233, etc., there is the method using the carboxylic acid as the reducing gas. According to this method, the copper wiring, etc. are reduced by causing locally the oxidation-reduction reaction while using the reducing gas and the oxidizing gas together, and then the burying is executed.
The PVD step is executed when the buried electrode is formed on the semiconductor substrate on which the underlying wiring made of the copper and the insulating layer for covering this wiring, for example, are formed, and the like. More concretely, the via hole is formed in the insulating layer at the buried-electrode forming position to expose the underlying wiring, and then the barrier metal is formed (film formation) in the via hole by the deposition using the PVD technology.
Then, the copper is buried in the via hole by the PVD technology, whereby the buried electrode that is connected to the underlying wiring is formed. The cleaning step is carried out to assure the electrical connection between the underlying wiring and the copper prior to the deposition of the barrier metal. More particularly, the surface of the underlying wiring is cleaned by the pre-process using the argon (Ar) sputter.
Also, in the CVD step, the SiN film of several hundreds nm thickness, etc. are deposited on the surface of the semiconductor substrate, for example, after the end of the CMP. This is to prevent the diffusion of the copper into the insulating layer from the underlying wiring and the buried electrode.
{circle around (3)} The Cleaning Step as the Post-process of the Etching Process
As described above, if the buried electrode connected to the underlying wiring is formed on the semiconductor substrate, the via hole is formed in the insulating film. The formation of the via hole is executed by providing the resist, that has the opening at the buried-electrode forming position, on the insulating layer and then etching the insulating layer while using the resist as a mask.
After the finish of this etching, the resist is removed by the ashing equipment and then the adhesion substance such as Si, C, Cu, etc. adhered onto the side wall of the via hole, etc. (referred to as xe2x80x9cdepo-substancexe2x80x9d hereinafter), that is not removed yet, is cleaned by using the chemicals. It is difficult to use the strong acid or the alkaline as the chemicals since the underlying wiring made of the copper is exposed in the via hole, so that the weak-acid cleaning is often employed.
{circle around (4)} The Cleaning Step as the Pre-process of the Packaging Process
For instance, in the step of jointing the electrode containing the copper as the major material, normally the method employing the solder as the joint material is employed. In such case, the oxide film is always formed on the surface of the copper electrode prior to the joint or at the time of joint. Since this copper oxide is inferior in conductivity, it is executed usually to remove such copper oxide by executing the cleaning process. As the cleaning method of the copper oxide, there is the method of removing the copper oxide by employing the carboxylic acid as the forming gas, as disclosed in Patent Application Publication (KOKAI) Hei 7-75699, etc., for example.
However, there are the problems described hereunder in the above cleaning methods in the prior art.
{circle around (1)} The Problem in the Cleaning Step as the Post-process of the CMP Step
As described above, in the cleaning step carried out as the post-process of the CMP step, the step of removing the particles and the step of removing the copper oxide on the insulating layer and the copper oxide formed on the copper wiring by the chemicals are carried out. When the process by using the chemicals is finished, the cleaning by the pure water is then performed to remove the chemicals.
However, there is the problem that the corrosion of the copper wiring, etc. is generated in the course during when the PH value of the chemicals is being changed from the acid to the neutral. This is because the slight etching proceeds on the overall surface of the copper wiring if the concentration of the chemicals is high, but the local etching occurs in the dilute solution.
FIG. 42 shows corrosions generated in the copper wiring, etc. having a 0.27 xcexcm width when the concentration of the chemicals (CIREX (product name) as the etchant in the example shown in FIG. 42) is changed. From FIG. 42, it is found that the corrosions are generated in compliance with the change in the concentration of the chemicals. Also, if a large quantity of dissolved oxygen is also present in the chemicals, the corrosion proceeds locally. Therefore, in the cleaning method in the prior art, there is the problem that the uniform etching cannot be achieved.
{circle around (2)} The Problem in the Cleaning Step as the Pre-process of the PVD Process and the CVD Process
As described above, since the cleaning step executed as the pre-process of the PVD process and the CVD process is the physical removing method by the Ar sputter, the contaminant adheres again onto the underlying wiring (made of the copper) exposed from the bottom of the via hole, and also the shoulder of the via hole formed in the insulating layer is scraped off by the sputter. Therefore, there is the problem that the formation of the fine buried electrode cannot be achieved.
Also, in the CVD step, the SiN film, or the like is deposited on the surface of the semiconductor substrate, as described above. In this case, since the copper wiring, etc. are exposed to the atmosphere in the period from the CMP to the deposition of the CVD film, the oxidation of the copper wiring, etc. is unavoidable. For this reason, prior to the deposition of the diffusion preventing film such as the SiN film, or the like, normally the plasma process using the reducing gas such as H2, NH3, or the like is performed as the pre-process in the CVD equipment.
This plasma process is done under the temperature environment close to 400xc2x0 C. Since such process is applied at the high temperature and in the state that the copper wiring, etc. are exposed, the copper surface is formed unevenly because of the recrystallization. Therefore, there is the problem that the coverage of the CVD film is locally degraded.
{circle around (3)} The Problem in the Cleaning Step as the Post-process of the Etching Process
As described above, the cleaning step executed after the etching process is mainly the cleaning step using the chemicals. But the cleaning action of this method is not sufficient. Therefore, there is the problem that the effective cleaning cannot be executed.
{circle around (4)} The Problem in the Cleaning Step as the Pre-process of the Packaging Process
As described above, in the prior art, the solder is employed as the joint material to joint the electrode made of the copper as the major material in the packaging. However, if the joint material whose resistivity is totally different from the electrode material is employed in transmitting the high speed signal, the reflection of the electromagnetic field is generated at that portion to disturb the high speed transmission. Therefore, it is desired that the different material should not be employed as much as possible to joint, otherwise the thinnest layer should be employed to the utmost to suppress the reflection of the signal if the different material is employed.
The present invention has been made in light of the above problems, and it is an object of the present invention to provide a solder jointing system which is capable of having a high processing capability and capable of preventing the re-oxidation or eliminating the danger of the explosion.
It is another object of the present invention to provide a solder jointing system and a solder jointing method which is capable of improving the throughput of the solder joint rather than the prior art, or preventing the generation of the residue on the substrate after the solder joint.
It is still another object of the present invention to provide a semiconductor device manufacturing method and a semiconductor device manufacturing system that is capable of removing uniformly and effectively the surface oxide film formed on the surface of the electrode or the wiring that contains the copper as the major material.
Also, it is yet still another object of the present invention to implement the good coverage in the film forming step that is carried out as the step subsequent to the cleaning step.
According to the present invention, the heating/melting areas and the carrying areas are provided in the chamber having the openings that are opened to the outer air, and in addition the formic-acid supplying means and the formic-acid exhausting mechanism are provided in the heating/melting areas.
Therefore, the low pressure atmosphere having the pressure distribution in which the lowest pressure is given in the heating/melting areas can be formed in the chamber, and also the temperature distribution in which the highest temperature is given in the heating/melting areas can be formed.
Accordingly, the oxides on the solder layers are removed by using the formic acid in the heating/melting areas, and also the formic acid is vaporized in the low pressure while jointing the solder layers by the heating and is removed by the exhausting mechanism. Since the exhaust and the inert gas supply are executed simultaneously in the heating/melting areas, the partial pressure of the formic acid is low but the vaporizing ability of the formic acid is high. If the formic acid is removed from the surface of the solder-adhered object in the chamber in this way, the re-oxidation of the solder layers on the solder-adhered object can be prevented.
Also, since the solder-adhered object can be loaded/unloaded into/from the chamber via the openings that are opened to the outer air, the processing ability of the solder jointing process can be increased. In addition, if the carrying areas are held by the heating means at the predetermined temperature, the vaporization of the formic acid can be accelerated.
In addition, the formic acid supplied to the heating/melting areas is introduced into the formic-acid decomposing mechanism, the formic-acid recovering mechanism, or the like by the exhausting mechanism in response to the pressure distribution in the chamber not to leak from the openings. Therefore, the environmental disruption due to the formic acid can be prevented.
Further, the solder-adhered object heated in the heating/melting areas is unloaded to the outside via the openings while falling its temperature in response to the temperature distribution in the chamber. Therefore, the solder-adhered object can be taken out from the chamber at the temperature close to the room temperature, and thus the handling of the solder-adhered object can be facilitated.
If the formic-acid supplying means supplies the formic acid to the heating/melting areas at the concentration of less than 75 vol %, the formic acid of such concentration can be used safely without the explosive limit.
Besides, if the air-stream controlling means are arranged to the boundaries between the heating/melting areas and the carrying areas, the coming and going of the gas between mutual areas becomes difficult. Thus, the pressure and the temperature can be held easily in respective areas and also the entering of the formic acid into the carrying areas can be prevented.
Since the holding mechanism of the solder-adhered object is provided in the heating/melting areas, the oxide film can be removed by the formic acid after the solder-adhered object is stopped/held so as to reduce variation in the temperature of the solder-adhered object and variation in the pressure. Therefore, the uniformity of the process applied to all the solder-adhered objects can be achieved.
Since the solder-adhered object is loaded/unloaded into/from the chamber by the conveyer belts, the continuous processing of the solder-adhered object can be attained and thus the processing efficiency can be enhanced. In addition, the solder-adhered object can be supplied intermittently into the chamber by using the above holding mechanism together, so that the productivity can be improved not to bring about the reduction in the quality.
According to the present invention, there are provided the magazine for containing a plurality of substrates having the metal pattern to which the solder layers are adhered thereon at a distance, and the heater arranged such that the magazine can be confined in the heater. Therefore, the solders on a plurality of substrates can be jointed at the same time and thus the throughput can be improved rather than the prior art.
Also, since the heater can be taken away not to surround the magazine after the solder layers are heated/melted by the heater, the temperature of the solder layers can be easily lowered and thus the time required from the heating to the cooling can be shortened. In addition, since the mechanism for fitting the cooling gas introducing mechanism to the heater is employed, the solder layers can be cooled more quickly by the cooling gas immediately after the heating of the solder layers is finished, and thus the solder cooling time can be shortened.
If the formic acid is supplied to the solder layers, the formic acid and the gas are mixed to suppress the excessive supply of the formic acid, or the formic acid is changed into the mists by the ultrasonic wave. Therefore, the excessive supply of the formic acid can be suppressed.
Further, since the magazine is placed only in the heating chamber, the adhesion of the pollutant in the air onto the magazine can be suppressed and thus the contamination of the substrates during the heating can be prevented.
Besides, since the heater and the magazine are confined in the heating chamber from the introduction of the formic acid into the heater to the exhaust thereof, the leakage of the formic acid from the heating chamber to the outside can be prevented.
According to the another present invention, the present invention has the feature that, in order to remove the oxide film (surface oxide film) formed on the surface of the electrode or the wiring containing the copper as the main material (the copper wiring, etc.), the surface oxide film is changed into the carboxylate and then reduced/removed. Accordingly, the removal of the surface oxide film can be executed uniformly and effectively not to give the physical and chemical damages to the copper wiring, etc. per se and their peripheral structures.
The surface oxide film is mainly formed of copper (II) oxide (CuO). Even if the surface oxide film is left as it is in the reductive hydrogen atmosphere, or the like, such surface oxide film is not reduced unless the temperature is increased to exceed 400xc2x0 C. or more. Therefore, in order to cause the copper surface to reduce quickly at the low temperature, such a reaction system is employed in the present invention that the surface is changed into the salt state having the high reactivity once and then the reduction of the copper is generated.
Also, in the present invention, the carboxylate is selected as the salt state having the high reactivity, and the formic acid is employed as the carboxylic acid gas used to form the carboxylate, and the heating of more than 200xc2x0 C. but less than 400xc2x0 C. is applied, for example.
The reaction when the formic acid is employed will be given as follows.
2HCOOH+CuOxe2x86x92(HCOO)2Cu+H2O 
(HCOO)2Cuxe2x86x92Cu+H2O+2CO2 
In this manner, since the formate is decomposed into H2O and CO2, the impurity does not remain on the semiconductor substrate, on which the copper wiring, etc. are formed, after the cleaning process. Thus, the formate has no influence upon the post-step of this cleaning process.
In contrast, various types (e.g., acetic acid) may be employed as the employed carboxylic acid if they can generate the copper and the carboxylate. However, the formic acid has the quickest reaction as the carboxylate, and thus it is preferable from this viewpoint to employ the formic acid. Also, in order to reduce the copper from the generated carboxylate, the reactive gas (e.g., the hydrogen, etc.) may be introduced.
Meanwhile, if the above carboxylic acid is employed to remove the surface oxide film, the environmental temperature in the removing process must be set properly in order to remove effectively the surface oxide film. Therefore, the inventors of the present invention examined the temperature conditions necessary for the reduction of the surface oxide film and then obtained the results shown in FIG. 43. It is considered from these results that, unless the atmospheric temperature for the reduction is more than 200xc2x0 C. but less than 400xc2x0 C., the sufficient reducing rate cannot be achieved and that this temperature may be the limit temperature in practical use because the growth of the copper crystal grain is accelerated at the temperature higher than this temperature to thus generate the surface unevenness.
On the contrary, in the structure of the semiconductor device manufacturing system, since the seizure (generation of the foreign matter) is caused when the droplets are adhered onto the insulating layer on the semiconductor substrate in introducing the carboxylic acid, a method of preventing this seizure is needed. Also, since the copper is the material that is ready to re-oxidize, a structure for preventing the re-oxidation is needed.
This respect can be overcome by spraying the carboxylic acid as the small-particle mists to change the sprayed carboxylic-acid mists into the vapor when the carboxylic acid is supplied to the copper wiring, etc. For example, the spray nozzle BIMK6004 manufactured by the Ikeuchi Co., Ltd. can spray the carboxylic acid having the particle diameter of 15 to 30 xcexcm in the air according to the conditions, and also the spray nozzle BIMV8002S can spray the carboxylic acid having the particle diameter of 10 to 20 xcexcm.
As other means, there may be employed a method of generating the vapor of the carboxylic acid by heating the gas (e.g., nitrogen gas) that is mixed into the carboxylic-acid mists. For example, the line heater L-00-100W manufactured by the Kikuchi Co., Ltd. can heat the gas up to 300xc2x0 C. at a gas flow rate of 12 liter/min at maximum.
In addition, there may be employed a method of generating the vapor indirectly by spraying the carboxylic-acid mists onto the hot plate, etc. In this case, the heater serving as the hot plate is heated to 250 to 300xc2x0 C., then the carboxylic-acid mists (e.g., the formic-acid mists) are sprayed onto this hot plate, and then the surface oxide film may be removed by the generated vapor.
Meanwhile, since there is a possibility of the explosion during the process according to the concentration of the carboxylic acid used to remove the copper oxide film, this possibility must be avoided. For example, if the formic acid is employed as the carboxylic acid, there is the danger of ignition/explosion by the trouble in the equipment because the formic acid has the flash point of 69xc2x0 C. at a volume concentration of 98%.
However, if the volume concentration is set to less than 76%, the flash point is lost and no danger of the explosion is present, nevertheless the reducing ability is not influenced. As a result, if the concentration of the carboxylic acid is set lower than the concentration at which the flash point does not exist (in the case of the formic acid, the volume concentration is 75%), the safety in the cleaning process can be improved.